Percutaneous needle procedures, such as needle biopsies, drainages, and other medical interventional procedures, are routinely performed using x-ray fluoroscopy-guided methods. In an attempt to reduce procedure time and radiation exposure, while improving targeting accuracy, the use of laser pointer devices has been proposed. A conventional laser pointer-based workflow may include four phases: image acquisition, medical interventional device (needle) trajectory planning, light pointer aligning, and needle puncture.
In the image acquisition phase, a three-dimensional (3D) image of the patient is either directly acquired using a C-arm CT system or a CT or MRI scanner. In the case of a 3D image obtained using the CT or MRI scanner, the 3D image must then be registered to a C-arm system.
The needle trajectory planning phase involves marking a target point (e.g., a tumor) and a suitable skin entry point on the 3D image The ideal needle trajectory is determined by a straight line that originates outside the patient's body and passes through the skin entry point and the target point.
The light pointer aligning phase involves aligning the light beam of a laser pointer with the needle trajectory determined by the above-described line. The spot of light generated on the skin of the patient's body provides a visible guide for needle placement.
In the needle puncture phase, the tip of the needle is placed on the laser light sot on the patient's skin and oriented such that the laser light spot is visible in the center of the needle hub. The needle is then advanced forward by keeping the laser light spot centered on the needle hub. The needle is commonly imaged in two-dimensions (2D) using x-ray fluoroscopy while it is advanced towards the target.
Several methods have been proposed for aligning the laser with the planned needle trajectory in the light pointer aligning phase. One particular class of methods uses a passive mechanical arm for holding the laser pointer device in place and x-ray fluoroscopy for aligning the laser pointer device.
An example of one method in this class associated with C-arm hybrid (2D/3D) imaging systems is known as the “bulls-eye view” or “down the beam/barrel view” method. This method includes four steps (after image acquisition and needle trajectory planning):                1. Isocentering the needle target on the C-arm system.        2. Rotating the C-arm so that the target point and skin entry point are collinear with the central x-ray beam (bulls-eye, down-the-beam view).        3. Aligning needle with the central x-ray beam.        4. Aligning the laser with the needle.        
In step 1, the C-arm system is adjusted such that the target point is as close as possible to the isocenter of the C-arm. This can be done by forward projecting the target point onto the detector of the system and placing a graphical marker (dot) at this position onto the live fluoroscopic image. This functionality is typically available with imaging systems with a known projection geometry (calibrated x-ray cameras). Then, the C-arm table is adjusted (in the x, y, and z directions) so that the dot appears in the center of the fluoroscopic image in two orthogonal views.
After the target point coincides with the isocenter, the C-arm is rotated in step 2 so that the central beam, passing from the x-ray source of the system through the isocenter to the center pixel of the detector, passes through the skin entry point as well. Under such a projection geometry, the target and skin entry points appear superimposed on top of each other and the central beam and the planned needle trajectory are collinear.
In step 3, the needle is aligned with central beam under live fluoroscopy by placing the needle tip over the graphical marker on the skin entry point and adjusting the orientation of the needle so that it projects to a point instead of a line.
Finally in step 4, the laser is aligned with the needle by keeping the needle in place, while adjusting the mechanical arm so that the laser light beam is collinear with the needle.
An improvement to this method has been proposed that eliminates one of the above mentioned four steps:                1. Isocentering.        2. Assuming bulls eye view.        3. Aligning laser with central beam.        
After isocentering and assuming the bulls-eye view, the laser is directly aligned with the central beam, without the need for placing the needle first under live fluoroscopy. This is done by simply placing the laser into the center of the detector, orthogonal to the detector plate by using a mechanical guide, which first needs to be attached to the detector and later removed.
There are shortcomings with both these methods. The first method is time consuming, placing the target point into the isocenter of the C-arm is difficult to achieve with adequate accuracy, and aligning the laser by first aligning the needle is cumbersome and time consuming and typically requires two persons to perform. The second method requires isocentering and the use of mechanical guides to align the laser.
Accordingly, a method and apparatus for aligning a laser pointing device with a pre-planned medical interventional device trajectory is needed that avoids the shortcomings of current methods and apparatus.